Thyroid Nodules
What is a thyroid nodule?
A thyroid nodule is a lump within the thyroid gland that is radiologically distinct from the surrounding thyroid tissue (picture1).
How are thyroid nodules assessed?
Picture 1. Arrow pointing to a solid thyroid nodule on an ultrasound image.
As with other endocrine glands, when assessing a thyroid nodule, both structure and function of the nodule should be evaluated. Structurally the nodules may be divided into cystic (fluid-filled), solid, or mixed solid/cystic. Ultrasound (US) scan is used to assess the structure of thyroid nodules. While most cystic nodules are benign, solid nodules may need further evaluation with biopsy to determine their malignant (cancerous) potential.
The function of thyroid nodules is often assessed with blood tests and nuclear medicine (NM) thyroid scan. Based on their appearance on the NM scan, thyroid nodules may be divided into cold (underactive), hot (overactive), or warm (similar function to the surrounding thyroid tissue).
Therefore, a thyroid US scan and a blood test for thyroid function are the minimum tests required when assessing patients with thyroid nodule(s). If the blood test shows hyperactive thyroid, a NM thyroid scan is also done to determine the cause of overactivity.
When thyroid nodules are assessed with US scan the so-called TI-RAD classification (Thyroid Imaging – Reporting & Date System) is used to determine their malignant potential and the need for follow up or biopsy. Each nodule is given a score of 1 to 5 based on its US features with increasing chance of malignancy with higher scores (Table 1).
Table 1. TI-RAD classification of thyroid nodules based on their ultrasound features.
How is thyroid biopsy done?
Picture 2. Thyroid biopsy is done with a thin need through the skin under ultrasound guidance.
Thyroid biopsy is done via “fine needle aspiration” (FNA) under US guidance. A very thin needle (smaller than the needle used to draw blood) is passed through the skin into the nodule under US guidance (Picture 2). The thyroid cells that become trapped inside the needle are spread on glass slides and sent to pathology for analysis under a microscope. Your doctor will receive the results often within 5 days.
What are possible results of thyroid nodule biopsy?
Pathologic analysis of thyroid FNA biopsy will result in one of the following 6 results:
Non-diagnostic: Simply enough cells were not obtained to arrive to a diagnosis. The chance of malignancy is 1-4%. A repeat FNA biopsy is recommended in about 3 months.
Benign: This is reassuring. US follow up may be recommended based on US findings.
Indeterminate: Risk of malignancy is 5-15%. Repeat FNA biopsy is recommended in about 3 months.
Follicular neoplasia: The only way to know if a follicular neoplasia is benign or malignant is to remove the entire nodule through a hemithyroidectomy (removal of the right or left half of thyroid containing the nodule) and send it for pathological assessment. The risk of malignancy in these nodules is 15-30%.
Suspicious for malignancy: The risk of malignancy is about 60-75%. At least a diagnostic hemithyroidectomy is required to confirm or rule out malignancy.
Malignant: Definitive treatment will be required. Your surgeon will discuss this with you which may include hemi- or total thyroidectomy with or without removal of neck lymph nodes.
What are the treatment options for hot nodules?
Picture 3. Arrow pointing to a solitary hot nodule in the right thyroid lobe on a nuclear medicine thyroid scan.
As mentioned above, thorough assessment of a thyroid nodule includes assessment of its structure using US as well assessment of its function. If the thyroid function test indicates thyrotoxicosis (hyperactive thyroid), a NM scan is done to identify the cause. In about 5% of the cases thyrotoxicosis is due to a solitary hot nodule (Picture 3).
The treatment options in such cases include:
Antithyroid medications indefinitely (least favourable)
Radioactive iodine: gives good results with a low dose and can also be repeated if necessary. It generally takes about 3-5 months to normalise thyroid function.
Surgery in the form of hemithyroidectomy controls thyrotoxicosis more quickly. It is the only viable option if there is suspicion for malignancy, or the nodule itself is symptomatic (cosmetic, or pressure symptoms).
Is surgery indicated for benign nodules with normal function?
Surgery may still be indicated for benign nodules that function normally. These indications include pressure symptoms such as difficulty breathing, chocking sensation, or difficulty swallowing. Patient may also request surgery for an unsightly thyroid lump, or the mere anxiety associated with ongoing monitoring.